Method for underground storage of heavy flowable substances

ABSTRACT

A method for underground storage of heavy liquid substances, such as No. 2 heavy fuel oil, which solidify at normal storage temperatures, in a storage facility including a series of parallel underground galleries separated by protective piers, the galleries being closed at one of their ends adjacent to a working gallery and opening at their other ends into a common central channel communicating with the well being worked, and the beds of the galleries being in the same substantially horizontal plane. The fuel oil is conveyed into the galleries and solidifies. In order to take the stored substance out of the storage facility, a fluid which may be water with fuel oil trapped in a basin or a portion of the solidified mass of fuel oil itself is heated and then circulated over the surface of the mass of solidified fuel oil. The fuel oil is thus progressively liquefied and entrained in the flow of the fluid so that it may be pumped and taken out of the storage facility.

United States Patent 1 1 de Jerphanion et a1.

[451 Sept. 23, 1975 Etienne Schlumberger, both of Paris, France [73]Assignee: Societe a Responsabilite Limitee:

Societe Francaise de Stockage Geologique GEOSTOCK", Paris, France [22]Filed: July 8, 1974 [21] Appl. No.: 486,697

[30] Foreign Application Priority Data July 10, 1973 France 73.25301[56] References Cited UNITED STATES PATENTS 3,874,399 4/1975 Ishihara137/13 FOREIGN PATENTS OR APPLICATIONS Sweden 61/.5

Primary ExaminerAlan Cohan Attorney, Agent, or FirmBaldwin, Wight &Brown [57] ABSTRACT A method for underground storage of heavy liquidsubstances, such as No. 2 heavy fuel oil, which solidify at normalstorage temperatures, in a storage facility including a series ofparallel underground galleries separated by protective piers, thegalleries being closed at one of their ends adjacent to a workinggallery and opening at their other ends into a common central channelcommunicating with the well being worked, and the beds of the galleriesbeing in the same substantially horizontal plane. The fuel oil isconveyed into the galleries and solidifies. In order to take the storedsubstance out of the storage facility, a fluid which may be water withfuel oil trapped in a basin or a portion of the solidified mass of fueloil itself is heated and then circulated over the surface of the mass ofsolidified fuel oil. The fuel oil is thus progressively liquefied andentrained in the flow of the fluid so that it may be pumped and takenout of the storage facility.

11 Claims, 4 Drawing Figures US Patent Sept. 23,1975 Sheet 1 01 43,906,973

F IG] US Patent Sept. 23,1975 Sheet 2 of4 3,906,973

S W Q 222222 h 2 3 N G 8 8 v, 1 R E US Patent Sept. 23,1975 Sheet 3 of4US Patent Sept. 23,1975

Sheet 4 of 4 METHOD FOR UNDERGROUND STORAGE OF HEAVY FLOWABLE SUBSTANCESThe present invention relates to the field of underground orsubterranean storage of heavy flowable or liquid substances such asheavy fuel oil, the viscosity characteristics of which are such that thesubstances congeal or solidify at normal storage temperatures.

At ordinary temperatures C to C) the viscosity of heavy fuel oil isknown to increase considerably, and it is necessary to heat up so thatit may be pumped. In conventional airborne storage, the heating up ofheavy fuel oil is effected by providing in metal tanks steam, water oroil heat exchangers which may be in service continuously or only duringeffective use.

On the other hand, with subterranean storage the method of heating bymeans of heating coils alone is not applicable by reason of thegeometrical configuration of the storage facility which generallycomprises very long galleries which become inaccessible after they areput into service and which would moreover require heating coils of verygreat length. Further, maintaining the heating coils at the requiredtemperatures demands prohibitive expenditures in energy.

German Pat. No. 1,033,139 is an example of prior art disclosuresconcerning the use of heating coils for such purposes. In this knownarrangement, the heating device is adapted to heat water which is undera layer of petroleum in a storage cavity.

In another prior art document, US. Pat No. 2.17.2,683, ores areextracted by a stream of liquid sulfur. It therefore concerns extractionof ores and nota method of storing and taking out of storage heavyliquid substances such'as fuel oil.

An aim of the present'invention is to overcome the problems of storingheavy fuel oil or any other substances having physicalcharacteristicswhich lead, t similar contraintsl Generally speaking, the methodaccording to the invention comprises circulating at least one hot fluidin contact with the exposed surface of the storedsubstance in congealedor solidified state and thereby entraining and progressively thawing orliquefying the stored substance so that it may be pumped and taken outof storage. I Y

A more specific object of the invention consists in a method for thesubterranean storage of heavy liquid substances solidified at normalstorage temperatures, and in particular No. 2 fuel oil comprising, witha view to storage, introducing the substance to be stored, previouslyheated if necessary, into a series of parallel subterranean galleriesseparated from their adjacent galleries by protective piers and beingthen closed at one end, the free ends of all the galleries opening intoa common central channel which is connected to a well being worked, thebeds or bottoms of all the galleries being located in substantially thesame horizontal plane, the substance thus stored being solidified insaid galleries; and, with a view for taking the substance out ofstorage, introducing a heated fluid through the ends of the galleriesopposite the central channel, said heated fluid coming into contact withthe surface of the stored substance and transferringheat thereto,thereby liquifying at least partially the stored substance and enablingit to be entrained by the stream of heated fluid towards the centralchannel, separating the-stored substance from the heated fluidentrainingit, and recovering by pumping the substance thus taken out ofstorage.

In a variation of the present method, the heated fluid used for takingthe substance out of storage is taken from thestored substance, in whichcase the fluid is the substance itself, means are provided in the midstof the stored substance for heating part of the stored substance andcirculating it.

It is, however, preferable to employ hot water as the heated fluid usedfor taking the substance out of storage that is, water previously heatedwhich is permanently found in the subterranean storage facility in thelower portion of the layer of the substance being stored. In this casethe hot water is immiscible with the stored substance and thereforeduring the process of taking the substance out of storage it must beseparated for example, by'settling from the thawed or liquefiedsubstance which it has entrained.

The invention will be illustrated by, but without being limited to, thefollowing detailed description, made with reference to the accompanyingdrawings, in which:

FIG. 1 schematically illustrates in horizontal cross: section thearrangement of the storage galleries;

FIG. 2 is a vertical sectional view illustrating the operation of themethod according to the invention;

FIG. 3 schematically illustrates a mock-up installation used forexperimental work on the method according to the invention; and

FIG. 4 is a graph showing the results obtained with the mock-upinstallation of FIG, 3.

In the example given by way of illustration in FIGS. 1 and 2, we areconcerned with the underground storage of No. 2 fuel oil. The storagefacility is located unnical, geotechnical and economic requirements. Asshown in FIG. 1, the rock mass 1 comprises a series of parallelgalleries, three such galleries being shown in the drawing. Thegalleries comprise gallery halves 2a, 2b, 3a, 3b, 4a and 4b and adaptedto be closed at one end (schematized by an *X") and opening at the otherend into a common central channel 5. The central channel-is incommunication with the well being worked to the side indicated by thearrow f (see FIG. 2). The series of gallery halves communicate with agallery 6, called theworking gallery, which communicates at its end onthe side of the arrow f-with the well being worked (see FIG. 2). Thegalleries are separated respectively by protective piers 7a, 7b, 8a, 8b,etc. The beds or bottoms of all the galleries are in the samesubstantially horizontal plane.

During the filling operation, the hot fuel oil from the well beingworked is introduced into the working gallery by pumping in thedirection of the arrow f. The fuel oil then flows into the galleryhalves 2a, 2b, 3a, 3b, 4a, 4b, etc. from their ends opposite the centralchannel 5.

Under normal storage conditions, the temperature in the galleries is inthe range of 10C to 20C. The hot fuel oil flows in at a high flow rateso that it cools off sufficiently slowly to retain rather'low viscosity,for example in the order of 300 cst at 50C, in order to be able tospread horizontally over the entire length of the galleries.

When the storage facility is full, the fuel oil may be allowed to cooloff completely even if the fuel oil is of the type having a very-highpoint of solidification. This possibility is particularly desirable inthe case of reserve storage facilities which therefore do notnecessitate any application of heat for as long as the fuel oil isstored, i.e., for several years.

This is interesting in the case of seasonal storage where the heating isonly carried out for the quantity of fuel oil desired and only for thetime requiredfor pumping.

The heating power to be employed to obtain the reheating at a given flowrate may be greater than that in the case of constant temperaturemaintenance, but the device only operates during a small part of the:year.

Another advantage of heating the stored substance cool off resides inthe fact that as a result of the lower heat loss in the ground owing tothe fact there is an insulating envelope of the solidified substanceabout a thawed or liquified mass of the substance and that the meantemperature of the substance is low, the mean temperature of the groundremains low which reduces the supplementary geomechanical stresses ofthermal origin in the rock mass. This advantage may be importantdepending on the rock in which the storage facility is dug, for it isthen possible to:

1. position the storage facility deeper in order to make it feasiblewhich would not be possible with a storage facility employing permanentheating; or

2. reduce the safety piers between galleries and thereby increase thepossible storage volume within a given perimeter.

The process of taking the substance out of storage will now be describedin greater detail with reference to FIG. 2. HO. 2 is a schematicvertical cross-section showing the installation provided about a wellbeing worked for carrying out the method according to the invention.

Reference numeral 9 at the right of FIG. 2 corresponds to the well beingworked. The line 9 represents the pipe for pumping hot fuel for storage.The well 9 also contains a pipe 11 which conveys the fuel oil for takingit out of the storage facility, and two pipes 12a and 12b for pumpingsubterranean water out of the facility: the pipe 120 for use when thestorage facility is dormant and the pipe 121: for use when subterraneanwater is previously used to heat the substance in storage, and a pipe 13for carrying fuel oil for heating. A pipe 35 is also provided forcarrying streams as will be described hereinafter. The well 9 containsmoreover all the usual operating pipes (for compressed air, aeration,etc.).

At the lower part of FIG. 2 a storage gallery 14 of the type illustratedin FIG. 1 is shown. The fuel oil is stored in the gallery 14, the levelof stored fuel-therein being represented by the line au. A small amountof water flows from the surrounding ground into the galleries. In fact,the pressure of the water in the surrounding ground is greater than thatof the fuel oil in the: storage facility which is at approximatelyatmospheric pressure. The rock mass is chosen to be as impermeable aspossible, but it is not completely impermeable and a certain quantity ofwater continually penetrates into the storage facility. This water flowstowards the bottom of the galleries towards a basin 15 where it issubjected to a first settling operation and then to the basin 19 whereit is subjected to a second settling operation. From there it is carriedaway and processed on the surface by pipes 22 and 12a. The subterraneanwater coming from the surrounding underground streams around under thesolidified substance along the gallery till it reaches the basin 15 intowhich .it eventually penetrates. By way of example, the basin 15 has alength in the order of 10 m whereas the galleries may be 500 m long. Thesections of the gallery 14 may be between 50 m'- and 400 m depending onthe nature of the rock in which the storage facility is formed. 7

The bottom of the basin 15 is below the bottom of the gallery so thatwater can be collected and can settle in the basin below the substancewater interface represented by the line bb. A pump 16 is immersed in-thebasin 15, and the pipe 17 connected to its delivery end divides into twolines 17a and 17b along which valves 18a and 1812 are respectivelyprovided. The line 17a terminates at a settling tank 19. The watersettled in the tank 19 is drawn via pipe 20 by the pump 21 whichdelivers the same to a pipe 22 communicating with the pipe 12a (or 12b)through valve 22a (or 2217). Further, the pipe 17b terminates'in aheat'exchanger'23. The water heated in the exchanger 23 leaves throughline 24 and arrives at a main pipe 25 for conveying the reheating fluidto the end of the gallery opposite basin 15 where it is introduced at25a.

The fuel oil circuit comprises a pump 26 immersed in the storedsubstance in the storage facility, the delivery pipe 27 for the pump 26arrives at a separator 28 after passing through a valve 29. Two linesbranch off from the separator 28, a secondary line 49 which collectswater which may have settled in the separator and carries it to thesettling tank 19 and a main pipe 11 for taking fuel oilout of thestorage facility. The fuel oil separated fromthe water in the settlingtank 19 is returned to the gallery via pipe 30.

Alternatively, the hot fuel oil at C taken from the basin 15 may be usedto heat up the fuel oil solidified in the galleries, to a temperature of45C for example.

For this purpose, the fuel oil circuit comprises a special deviceoperatingin conjunction'with the separator 28 enabling at the outlet endof the pipe 27 the adjustment of the overall flow rate of fuel oil, asdesired, in

two directions.

The first direction is the above-described direction in which a portionof the fuel oil is brought to the surface over pipe' 11.

The second direction, after valves 32 and 34, follows the pipes 33 and25 terminating at the closed ends of the galleries. The flowrecirculating in this manner (at 80C for example) is adjusted so as toobtain the liquefaction (at 45C for example) of the fuel oil being takenout of storage. It will be noted that the valve 32a on the pipe 10 mustbe closed during the circulation of hot fuel oil.

The reheating circuit comprises a steam circuit 35 with theaforementioned heat exchanger 23 and another exchanger 36 for thepetroleum for reheating. The petroleum for reheating is introduced viapipe 13 terminating at the tank 37. The petroleum for reheating iscarried via pipe 38 through a series of heat exchangers 39 in the midstof the mass of stored fuel oil 14 before passing over line 40 drawn by apump 41 which de- -livers the petroleum through the exchanger 36 beforecarrying it back to the tank 37 over line 42.

The operation of the installation shown schematically operate on themineral oil (petroleum) for reheating introduced along pipe 13 andcirculating in closed circuit through the pumps 42, heat exchanger 36and tank 37. The heat exchangers 39 enable the temperature of the fueloil in the basin 15 to be raised to about 70C The removal of the No. 2heavy fuel oil is effected after the reheating with a circulation of hotwater in accordanee with the present invention.

When the storage facility is operative i.c., when the stored fuel oil isbeing taken out of storage, the'water collected in the basin 15 isreheated in the heat exchangers 23 and directed towards the closed endsof the galleries via pipe 25.

From there the water circulates along the surface of the solidified fueloil towards the central channel and the basin 15. This hot waterliquefies a film of fuel oil along the outer surface of the mass ofsolidified fuel oil which is set in motion with the hot water in thedirec tion towards the central channel 5 and the basin 15.

The reheating of themass of fuel oil in storage with the hot waterraises the temperature of the surface portion thereof to a value justhigh enough for it to flow to the basin 15, for example.

As a result of the preliminary operation of the exchangers 39, the fueloil in the basin is completely liquified when the circulation of the hotwater is begun. The liquid water-fuel oil mixture which is formedtherefore separates properly. The length of the basin is designed sothat the fuel oil has sufficient retention time before being drawn awayby the pumps 26 and carried to the surface. 7

The volume of water retained in the basin 15 is calculated so that thereis a suffieient quantity of water to ensure the entire circulation.

In order to avoid very high water and heating power requirements whenthe process of taking the stored substance out of storage is begun, thehot water may be circulated along only several galleries or along onlythe portions of the galleries in proximity to the basin 15.

After the water originating from the basin 15 has been used to reheatthe fuel oil, it is carried to the surface via pipe 121; to a specialprocessing circuit.

Alternatively, the method according to the invention could operate witha heating fluid other than water which would be of particular interestin case it would not be possible to use water to reheat the storedsubstance. In the present example, it is advantageous to use some of thesubstance, i.c., the fuel oil per se, as the reheating fluid as shown inFIG. 2.

Generally speaking, however. hot water is preferred as the reheatingfluid, for, all things being equal, the efficieney of heat transferbetween hot water and the solidified stored subtance is ten timesgreater than that of hot fuel oil with the solidified stored substance.As water is heavier than the fuel oil, water is permenantly deposited onthe surface of the mass of solidified fuel oil which further increasesthe heat transfer therebetween. It is nevertheless desirable to providea hot fuel oil circuit for reheating the solidified substance in case ofnecessity, e.g., if and when the hot water circuit is out of order.

It will be noted that the installation described with respect to FIG. 2does not include any piping or equipment in the galleries. The basin l5and the pumping and reheating equipment are all grouped around the baseof the well. Nearly all the pipes and valves are disposed in the workinggalleries of narrow cross-section, accessible to workmen.

FIG. 3 schematically illustrates the mock-up of the installation inwhich pilot tests of the method according to the invention were carriedout; This series of tests was essentially intented to measure in amock-up speed of liquefaction of various qualities of fuel oil,including heavy fuel oil No. 2, as a function flow rate and temperatureof the hot water used.

The working gallery (reference 14 in FIG. 2) is represented by a part ofa tank having an anterior plate 51 whereas the basin (reference 15 inFIG. 2) is represented by the residual .part 52 of the tank.

The solidified fuel oil 53 is stored in part 50 of the tank. For filingwith fuel oil there is a movable vertical partition 54 on top of theplate 51. When the fuel oil is solidified the partition 54 is removed,the fuel oil then forming a practically solid block or mass 53 of fueloil. The height h of the block 53 is shown in the drawing. The topsurface of the block 53 physically represents the line aa. Thecombination of the two parts 50 and 52 of the tank is about l0 meterslong. Another plate 55 erected in the part 52 is used to separate thepart 56 for volume of water from part 57 for the fuel oil taken out ofstorage as will be seen hereinbelow.

At the extreme left of FIG. 3 and above the block 53 is provided a spraydevice 58 for supplying hot water in the form of a shower. The watercircuit comprises a pump 59 communicating with a reservoir or tank (notshown) through a combination of valves 60 and pipes 61. The pipe 62conveys flow rate Q of hot water to the spray device 58. A sensor 63 isprovided on the pipe 62 for temperature regulation. Water collected at56 (approximate flow rate Q) is recycled via pipe 64 through valve 65,reheater 66 and flow rate measuring device 67 (schematically representedby a venturi tube).

The fuel oil removed from storage (flow rate q) is collected in part 57of the tank and recovered via line 68. A device 69 measures the flowrate q. The fuel oil is collected in recovery tank 70. At the bottom ofthe recovery tank 70 a drain valve 71 is provided for discharging wastewater collected therein. Likewise a tube 72 connects the lower end ofthe recovery tank to the main water recycling pipe 64.

The mock-up installation illustrated in FIG. 3 serves as a model for themethod according to the invention.

Hot water at a flow rate Q and a temperature Te is carried by the pipe62 to the spray device 58 which sprays it onto the block 53 ofsolidified fuel oil, the upper surface of the block 53 representing theline aa.

The hot water flows towards part 52 of the tank transferring some of itscalories to the fuel oil, the upper part of the block of fuel oil isthus liquified. The liquified fuel oil thus formed rises to the surfaceof the water, owing to the difference in densities, and flows into parts56-57 of the tank where hot water at a flow rate Q and a temperature Tslower than Te and liquid fuel oil at a flow rate q and a temperature Tsare collected. The dimensions of parts 56 and 57 of the tank arecalculated so that the retention time of the waterfuel oil mixture issufficient for the water and the fuel oil to be completely separatedvertically of the partition 55.

The speed of liquefaction may be measured by the magnitude dh/dt whichrepresents the variation of the height /z of the block of solidifiedfuel oil as a function of time t.

FIG. 4 shows a graph in which values of the temperature Te of the waterat the spray device 58 are given along the X-axis and values of themagnitude dh/dt in cm/hr are given along the Y-axis for showing thechange of this speed as a function of temperature for substantiallyconstant rate of flow Q of water equal to 0.27 liter/seczWe see that thespeed of liquefaction increases steadily with the temperature of thewater. The tests carried out on the mock-up installation demonstrate thepracticability of the method according to the invention.

Several advantages of the method according to the invention will now bementioned in addition to those already mentioned above.

The storage facility according to the invention may be provided for verylarge quantities of heavy fuel oil, for example in the order of amillion cubic meters. The invention brings about savings of -40 overconventional surface storage facilities. In comparison to present-dayunderground storage facilities, the novel process according to theinvention has much lower operating costs since it eliminates thenecessity of constantly supplying heat to the stored substance.

From the ecological point of view, underground storage is greatlypreferred over surface storage which requires large capacity tanks. Themethod according to the invention also offers absolute safety againstfire. Even if the stored substance comes in contact with a source ofcombustion, the fire will be stopped immedi-' ately owing to the absenceof air in the galleries.

What we claim is:

l. A method for underground storage of heavy flowable substancessolidified at normal storage temperatures in a storage facilityincluding a series of parallel underground galleries, closed at one oftheir ends, the open ends of the galleries opening into a common centralchannel, the bottoms of the galleries being substantially in the samehorizontal plane; comprising the following steps for putting thesubstance in storage, including introducing the heavy substance into thegalleries and letting said heavy substance thus stored in the galleriessolidify therein; and comprising the following steps for taking thestored solidified substance out of storage, including introducing a hotfluid through the ends of the galleries closed during the introductionof the heavy liquid substance, circulating said hot fluid in contactwith the solidified stored substance in the galleries towards the commoncentral channel and transferring heat to the solidified stored substancethereby progressively liquefying at least part of the solidifiedsubstance and entraining it with the circulating hot fluid, whereby thethen liquefied substance may be pumped and taken out of the storagefacility. A

2. A method according to claim 1, wherein the heavy flowable substanceis No. 2 heavyfuel oil (having a kinetic viscosity between 1 10 and 380centistokes at 50C). y

3. A method according to claim I, wherein the heavy flowable substanceis heated before being introduced into the galleries.

4. A method according to claim 1, further comprising separating theliquefied stored substance from the hot fluid with which it isentrained.

5. A method according to claim 4, further comprising, 1 after separatingthe liquefied stored substance from the hot fluid, pumping away theseparated liquefied substance.

6. A method according to claim 1, wherein the hot fluid is hot water,andfurther comprising collecting water in the storage facility under thestored substance and heating the collected water before circulating it.

7. A method according to claim 3, wherein the hot fluid is hot waterandwhereinthe separation is effected by settling. I

8. A method according to claim 1, further comprising reheating a portionof the stored substance, the hot fluid being constituted by the reheatedportion of the stored substance.

9. A method according to claim 6, further comprising immediately beforethe steps for taking the stored substance out of storage, circulating aseparate reheating fluid in a closed circuit including a heat exchangerthrough a solidified mass of the substance with subterranean waterthereby liquefying .the solidified mass then finding its way into abasin in communication with one of the galleries.

10. A method according to claim 9, wherein the reheating fluid iscirculated over only a few galleries of the storagefacility.

ll. Amethod according to claim 9, wherein the reheating fluid iscirculated over only the part of the galleries in the proximity of thebasin.

1. A method for underground storage of heavy flowable substancessolidified at normal storage temperatures in a storage facilityincluding a series of parallel underground galleries, closed at one oftheir ends, the open ends of the galleries opening into a common centralchannel, the bottoms of the galleries being substantially in the samehorizontal plane; comprising the following steps for putting thesubstance in storage, including introducing the heavy substance into thegalleries and letting said heavy substance thus stored in the galleriessolidify therein; and comprising the following steps for taking thestored solidified substance out of storage, including introducing a hotfluid through the ends of the galleries closed during the introductionof the heavy liquid substance, circulating said hot fluid in contactwith the solidified stored substance in the galleries towards the commoncentral channel and transferring heat to the solidified stored substancethereby progressively liquefying at least part of the solidifiedsubstance and entraining it with the circulating hot fluid, whereby thethen liquefied substance may be pumped and taken out of the storagefacility.
 2. A method according to claim 1, wherein the heavy flowablesubstance is No. 2 heavy fuel oil (having a kinetic viscosity between110 and 380 centistokes at 50*C).
 3. A method according to claim 1,wherein the heavy flowable substance is heated before being introducedinto the galleries.
 4. A method according to claim 1, further comprisingseparating the liquefied stored substance from the hot fluid with whichit is entrained.
 5. A method according to claim 4, further comprising,after separating the liquefied stored substance from the hot fluid,pumping away the separated liquefied substance.
 6. A method according toclaim 1, wherein the hot fluid is hot water, and further comprisingcollecting water in the storage facility under the stored substance andheating the collected water before circulating it.
 7. A method accordingto claim 3, wherein the hot fluid is hot water and wherein theseparation is effected by settling.
 8. A method according to claim 1,further comprising reheating a portion of the stored substance, the hotfluid being constituted by the reheated portion of the stored substance.9. A method according to claim 6, further comprising immediately beforethe steps for taking the stored substance out of storage, circulating aseparate reheating fluid in a closed circuit including a heat exchangerthrough a solidified mass of the substance with subterranean waterthereby liquefying the solidified mass then finding its way into a basinin communication with one of the galleries.
 10. A method according toclaim 9, wherein the reheating fluid is circulated over only a fewgalleries of the storage facility.
 11. A method according to claim 9,wherein the reheating fluid is circulated over only the part of thegalleries in the proximity of the basin.